1. Field of the Invention
The present invention relates in general to center boost engines for use with aircraft having multiple main power plants; and, more particularly, to an aeroplane center boost engine of the type mounted within the tail portion of the aeroplane and having a rearwardly facing exhaust nozzle at the aft end of the aircraft's empennage body structure, and a retractable/deployable fairing member surrounding the exhaust nozzle and capable of being shifted rearwardly relative to the exhaust nozzle into a deployed state in which the fairing member forms a truncated cone having a reduced nozzle exit opening and a parting line coincident the keel line of the nozzle. Thus, the retractable/deployable fairing member serves to reduce the size of the exhaust nozzle and empennage outlets when the center boost engine is inoperative; but, can be readily retracted into an expanded or stressed position surrounding the exhaust nozzle when the center boost engine is in operation--normally during take-offs, air refueling operations, and in certain emergency situations. The type of center boost engine here under consideration is commonly employed in certain military aircraft such, for example, as bombers.
Since center boost engines of the foregoing character are only operated during certain periods of in-flight operation, a need has long existed and has been recognized for providing some means for compensating for and, preferably, for eliminating, the undesired drag that is created by the engine inlet and the exhaust nozzle for such an engine. However, prior to the advent of the present invention, there has been no satisfactory solution to the drag problems created with center boost engines--in large part because the provision of deployable and/or retractable fairing structures has required complex and expensive mechanical configurations which, by their very nature, have required dedication of significant amounts of aircraft structure and volumetric storage space for the fairing components when not in use. Moreover, the use of such additional structural components tends to not only involve complex structure and actuating mechanisms, but, moreover, such proposed arrangements have generally tended to significantly increase the base weight of the aircraft, as well as to increase the very drag components that such systems are intended to minimize. The present invention relates specifically to a simple, yet highly effective, system for overcoming the foregoing problems and for providing a retractable/deployable fairing member capable of reducing the size of the exhaust nozzle and empennage outlets when the center boost engine is shut down so as to minimize the base drag characteristics of the empennage body structure. Those persons interested in the details of an improved aerodynamically faired deployable inlet for such center boost engine installations are referred to the aforesaid copending application, Ser. No. 306,748, filed Sept. 29, 1981, for "Deployable Inlet for Aeroplane Center Boost Engine."
2. Description of the Prior Art
The use of auxililary jet propulsion engines which are not intended for continuous use in flight has long been known in the prior art. For example, in U.S. Pat. No. 2,810,534--Fandeux, the patentee discloses the use of an auxiliary engine carried within a streamlined nacelle mounted beneath the fuselage of a twin propeller-driven aircraft. Although the nacelle is streamlined, presumably to reduce drag, the patentee does not discuss the desirability of being able to selectively open and/or close the auxiliary engine air inlet for the exhaust nozzle.
Another early patent of general interest in U.S. Pat. No. 2,557,522--Vautier, which, although not relating to the use of an auxiliary engine, is of interest for its disclosure of a pair of engines mounted within the fuselage and provided with air through a centrally disposed air inlet mounted on the upper surface of the aircraft fuselage forward of the vertical stabilizer. The patentee does not disclose any means for selectively opening or closing either the air inlet or the exhaust nozzle.
U.S. Pat. No. 3,237,891--Wotton, discloses an aircraft propelled by three turbo-fan engines, one of which is disposed within the engine fuselage beneath the vertical stabilizer, and the other two of which are mounted outboard of the engine fuselage. No reference is made as to the contemplated use of the centrally disposed engine as a "center-boost" or auxiliary jet engine. The central engine is supplied with air through an air inlet mounted forward of, and at the root of, the vertical stabilizer. No provision is made for selectively opening or closing either the air inlet or the exhaust nozzle.
Other patents of general interest are U.S. Pat. Nos. 3,134,561--Clejan, and 4,130,258--Fox. Each of these patents disclose aircraft having auxiliary power units which are retractably mounted so that they can be retracted into the aircraft fuselage when not in use.
A further disclosure of general interest is that contained in U.S. Pat. No. 3,109,610--Quenzler et al., a patent assigned to the assignee of the present invention. This patent discloses an aircraft having three jet engines, one of which is mounted within the fuselage and the other two of which are mounted outboard thereof. The central engine is provided with a centrally located air inlet scoop along the bottom longitudinal axis of the fuselage. The patentees are here principally concerned with the problems associated with ingestion of foreign material into the central engine; and, to inhibit this, they provide a pivoted flap at the forward end of the air scoop. However, such flap is intended only to inhibit entry of foreign material into the air scoop and is not intended to, nor capable of, closing off the air inlet or minimizing drag. Again, no provision is made in this patent for closing the center engine exhaust nozzle so as to minimize drag.
Keenan et al. U.S. Pat. No. 3,279,191 describes an aircraft gas turbine power plant comprising a main engine having a main centrally located air intake and a pair of auxiliary engines located outboard thereof. The air inlets to the auxiliary engines communicate with the main engine air inlet; and, pivoted doors are provided for closing the auxiliary air inlets when the auxiliary engines are not in use.
U.S. Pat. No. 3,489,377--Pearson et al. discloses an arrangement wherein an aircraft is provided with two outboard main propulsion engines and a centrally located auxiliary gas turbine engine. The center auxiliary engine is provided with a pair of air inlets and a pair of alternatively usable exhaut gas outlets, one of which is directed rearwardly and the other of which is directly vertically upward. The air inlets for the center engine are provided with hinged doors which can be opened either inwardly or outwardly and are designed so as to produce minimum drag on the aircraft when the doors are open in flight.
U.S. Pat. No. 3,472,029--Colley, is of interest for its disclosure of an auxiliary engine having a pair of air inlets located within the air inlet for the main engine, and a single downwardly directed exhaust gas outlet. A hinged closure member is provided for closing the exhaust gas outlet when the auxiliary engine is not in use.
Ward U.S. Pat. No. 3,172,623 is of interest for its disclosure of an aircraft having a central main power plant with a forwardly directed, laterally divided, air intake. A pair of streamlined pods are suspended from the delta-shaped wing of the aircraft on either side of the fuselage. Each pod contains a pair of jet engines with one engine in each pair having a forwardly facing air inlet and the other engine in each pair having a rearwardly facing air inlet. Both engines in each pod have coaxial exhaust nozzles with means to direct the exhaust gases vertically downward. The forward ends of each pod are provided with a pair of pivotally mounted doors which are in a closed position when the forward pod engines are not operating and which may be opened like the upper and lower jaws of a mount when it is desired to operate the forward engines. Similarly, both pods are provided with second pairs of pivotally mounted doors which can be moved between opened and closed positions so as to define air inlet scoops for the rearmost engines in the pods when the doors are open.
Two other references are of incidental interest are Axiehla et al. U.S. Pat. No. 3,592,414 and Tharratt U.S. Pat. No. 2,506,976. The Axiehla et al. patent discloses an adjustable tail cone assembly which is located between adjacent variable area jet engine nozzles and which is adjustable to provide a relatively smooth transition zone between the exterior surface of the tail and the nozzles. Tharratt is of interest merely for its disclosure of hinged panels in the aircraft fuselage which may be pivoted to an open position to permit ejection of rockets.
Unfortunately, however, systems of the foregoing types simply have not effectively dealt with, nor solved, the problems of increased drag associated with the exhaust nozzles of auxiliary jet engines which are normally inoperative during cruise conditions of the aircraft.